The present invention relates to the field of voltage regulators, and, more particularly, to voltage regulators of a type delivering a constant DC voltage while being supplied with a DC voltage prone to variation.
Conventionally, a regulator which is required to output a voltage of 3.3 volts will be supplied with a DC voltage of about 5.1 to 9.5 volts. The upper limit of supply of a regulator depends essentially on the technology of the active components with which it is provided.
An object of the present invention is to provide a voltage regulator which is not damaged when the voltage to which it is subjected exceeds the breakdown voltage of its active components.
A regulating device according to present the invention is supplied with a variable voltage Vv and delivers a constant voltage for supplying consumer elements. The device may include a regulating element, a means or circuit for comparing the variable voltage Vv with a reference voltage Vref, a means or circuit for dividing the variable voltage Vv by a factor k1, and a switching means or circuit able to supply the regulating element with a voltage Vr equal either to the variable voltage Vv, or to the divided variable voltage Vv/k1. The switching means may be controlled by the comparison means in such a way that the regulating element is supplied with the variable voltage Vv if a voltage condition is satisfied and with the divided variable voltage Vv/k1 if the voltage condition is not satisfied. This is because the variable voltage Vv is prone to take values greater than those which the active components of the device are capable of supporting.
Advantageously, the comparison means may include a means or circuit for dividing the variable voltage Vv by a factor k2 to obtain a comparison voltage Vcomp=Vv/k2, and an amplifier arranged as a comparator receiving on one input the comparison voltage Vcomp and on another input the reference voltage Vref to output a control signal V+. The control signal V+ may be of a conventional value 1 if the comparison voltage Vcomp is greater than the reference voltage Vref and of a conventional value 0 if the comparison voltage Vcomp is less than the reference voltage Vref.
The device may include an inverter at the output of the amplifier to obtain an inverse control signal Vxe2x88x92. The means for dividing by the factor k2 may include at least two resistors arranged in series between the variable voltage Vv and ground. The means for dividing by the factor k1 may include at least two resistors arranged in series between the variable voltage Vv and ground. The means for dividing by the factor k1 and the means for dividing by the factor k2 may include at least one common resistor.
Advantageously, the switching means may include a first transistor, one terminal of which is connected to the input of the switching means and sees the variable voltage Vv. Another terminal of the first transistor is connected to the output of the switching means and sees the voltage Vr. A control terminal of the first transistor is linked to a control means or circuit generating a voltage able to turn on the first transistor if the voltage condition is not satisfied or to turn off the transistor if the voltage condition is satisfied. The first transistor may be a MOS transistor.
The switching means may also include at least one second transistor, one terminal of which is connected to the input of the switching means and sees the variable voltage Vv. Another terminal of the second transistor is connected to the output of the switching means and sees the voltage Vr. Furthermore, a control terminal of the second transistor sees a control voltage equal to the divided variable voltage Vv/k1 that is able to turn off the second transistor if the voltage condition is not satisfied and to turn on the second transistor if the voltage condition is satisfied. Thus, the voltage Vr is equal to the divided variable voltage Vv/k1. The second transistor may be replaced by a cascode arrangement of several transistors, for example bipolar transistors, to deliver more current at the output of the switching means.
Advantageously, the means for controlling the first transistor may include a third transistor controlled by an output voltage from the comparison means and a fourth transistor controlled by the inverse of the output voltage from the comparison means. The third transistor may be connected at one terminal to ground and at another terminal to the output of the switching means seeing the voltage Vr by way of two resistors R21 and R22 in series. A common point shared by the two resistors sees the voltage Vr if the voltage condition is not satisfied and a voltage equal to Vr*R21/(R21+R22) if the voltage condition is satisfied.
The fourth transistor may be connected by one terminal to ground and by another terminal to the output of the switching means by a fifth transistor whose control terminal is connected to the common point shared by the two resistors. The fifth transistor may be on if the voltage condition is satisfied and off if the voltage condition is not satisfied so that the common point shared by the fourth and fifth transistors sees a voltage which is substantially 0 if the voltage condition is not satisfied and substantially equal to the voltage Vr if the voltage condition is satisfied. The third and fourth transistors may be MOS transistors with their sources connected to ground. The fifth transistor may also be a MOS transistor with a source connected to the voltage Vr.
Advantageously, the means for controlling the first transistor may furthermore include a sixth transistor having a terminal connected to the common point shared by the fourth and fifth transistors. The other terminal and the control terminal of the sixth transistor may be short circuited and linked to the output of the switching means seeing the voltage Vr by two resistors R27 and R28 in series. The sixth transistor may be on if the voltage condition is not satisfied and off if the voltage condition is satisfied. The common point shared by the two resistors R27 and R28 sees the voltage Vr*R27/(R27+R28) if the voltage condition is not satisfied and the voltage Vr if the voltage condition is satisfied.
A seventh transistor is provided with a control terminal connected to the common point shared by the two resistors R27 and R28. A terminal thereof may be connected to the common point shared by the fourth and fifth transistors. Another terminal of the seventh transistor may be connected to the common point shared by the fourth and fifth transistors by a resistor R33. Also, the remaining terminal of the seventh transistor may be connected to the control terminal of the first transistor of the switching means by a resistor R32. A resistor R31 links the control terminal of the first transistor and the input of the switching means which sees the variable voltage Vv.
This is done in such a way that the seventh transistor is on if the voltage condition is not satisfied (the control terminal of the first transistor being subjected to a voltage substantially equal to Vv*R32/(R31+R32) able to turn it on) and that the seventh transistor is off if the voltage condition is satisfied (the control terminal of the first transistor being subjected to a voltage substantially equal to Vv able to turn it off). The sixth transistor may be a bipolar transistor with short-circuited collector and base. The seventh transistor may be a bipolar transistor with the collector linked to the common point shared by the resistors R32 and R33.
By way of example, a regulator may be embodied in HF5 CMOS technology for which the breakdown voltage is about 15 volts. The general principle is to detect the voltage applied with respect to a threshold of 12.5 volts by a resistive bridge and a comparator, and to switch the regulating structure while maintaining normal operation if the voltage is below 12 volts and by dividing the voltage applied if it is greater than 12 volts. Thus, not only is the regulator protected against destruction in the event of an excessive supply voltage, but additionally the regulator continues to operate satisfactorily at a voltage above the breakdown voltage. The regulator is designed in such a way that none of its components prone to break down at about 15 volts are subjected to such a voltage.
A regulating process according to the invention provides a constant voltage for supplying consumer elements from a variable voltage Vv, in which process the variable voltage Vv is compared with a reference voltage Vref, the variable voltage Vv is divided by a factor k1, and the regulating element is supplied with an equal voltage Vr either via the variable voltage Vv or via the divided variable voltage Vv/k1 by switching between the two voltages. The switching may be controlled as a function of the comparison in such a way that the regulating element is supplied with the variable voltage Vv if a voltage condition is not satisfied and with the divided variable voltage Vv/k1 if the voltage condition is satisfied. The variable voltage Vv is prone to take values greater than those which the active components of the device are capable of supporting.
The invention also applies to the automobile field, and in particular to inflatable safety bags. Thus, it is possible to construct a regulator which supports a supply voltage greater than that normally permitted by the technology used. This exhibits numerous advantages in terms of choice of technology, reduction of the silicon area used and optimization. Indeed, in the case of an automobile, the regulator is normally supplied from a battery or an alternator operating at 12 volts. However, should the battery be unplugged, the output voltage from the alternator could reach much higher values. The electrical network of the vehicle is also subjected to radiation due to the high voltage used by the ignition spark plugs of the engine. As a result, a regulator mounted in an automobile must be able to support voltages of up to 25 volts.